Example

Solving 7.8x+4=5.4x87.8x + 4 = 5.4x - 8 by Collecting Variables and Constants

To solve 7.8x+4=5.4x87.8x + 4 = 5.4x - 8, observe that variable terms (7.8x7.8x and 5.4x5.4x) and constant terms (44 and 8-8) appear on both sides of the equation. Because 7.8>5.47.8 > 5.4, designate the left side as the variable side and the right side as the constant side.

Step 1 — Remove the variable term from the constant side: Since 5.4x5.4x is on the constant side, subtract 5.4x5.4x from both sides using the Subtraction Property of Equality:

7.8x5.4x+4=5.4x5.4x87.8x - 5.4x + 4 = 5.4x - 5.4x - 8

Combine like terms on the left by subtracting the decimal coefficients: 7.85.4=2.47.8 - 5.4 = 2.4. The equation simplifies to 2.4x+4=82.4x + 4 = -8. Now the variable appears only on the left.

Step 2 — Remove the constant from the variable side: The constant 44 is on the variable side, so subtract 44 from both sides:

2.4x+44=842.4x + 4 - 4 = -8 - 4

2.4x=122.4x = -12

Step 3 — Isolate the variable using the Division Property of Equality: Because xx is multiplied by the decimal coefficient 2.42.4, divide both sides by 2.42.4:

2.4x2.4=122.4\frac{2.4x}{2.4} = \frac{-12}{2.4}

x=5x = -5

Step 4 — Check by substitution: Replace xx with 5-5 in the original equation:

7.8(5)+4=?5.4(5)87.8(-5) + 4 \stackrel{?}{=} 5.4(-5) - 8

39+4=?278-39 + 4 \stackrel{?}{=} -27 - 8

35=35-35 = -35 \checkmark

Because both sides are equal, x=5x = -5 is confirmed as the correct solution. This example demonstrates that the collecting technique applies identically when the coefficients are decimals rather than integers or fractions. Subtracting decimal coefficients (7.85.4=2.47.8 - 5.4 = 2.4) and dividing by a decimal (12÷2.4=5-12 \div 2.4 = -5) follow the same arithmetic rules used for whole numbers, so the overall strategy remains unchanged.

0

1

Updated 2026-04-21

Contributors are:

Who are from:

Tags

OpenStax

Elementary Algebra @ OpenStax

Ch.2 Solving Linear Equations and Inequalities - Elementary Algebra @ OpenStax

Algebra

Math

Prealgebra

Related
Learn After